Trace-Cobalt Surface Engineering of Ni-Rich Co-Free Cathodes Unlocks High-Power Density and Long-Cycle Life in Pouch-Type Li-Ion Batteries

Layered Ni-rich Co-free cathodes offer compelling advantages in energy density and cost-effectiveness, but their practical deployment is significantly hindered by structural instability and sluggish charge transfer kinetics. Herein, we report a spinel Li_1-xCoO₂ surface-engineered LiNi_0.92Mn_0.05Al_0.03O₂ (Co-NMA) cathode with only ∼2000 ppm Co, in which the efficient utilization of trace Co dramatically enhances both structural integrity and interfacial reaction kinetics. Comprehensive in/ex situ spectrochemical analyses reveal that surface engineering effectively suppresses parasitic interface reactions with negligible O₂/CO₂ emission in the first charge process. Concurrently, spinel Li_1-xCoO₂ facilitates faster Li⁺ diffusion and electron transfer, resulting in lower electrochemical polarization and higher phase-transition reversibility. Consequently, the Co-NMA delivers a high reversible capacity of 225.3 mAh g^-1 at 0.1C and an initial Coulombic efficiency of 93.4%. It retains 62.1% of its capacity retention even at 10C, greatly outperforming the corresponding quaternary NMCA (54.2%) and NMA (49.1%). In pouch-type full cells, the Co-NMA sustains an extended cycle life over 650 cycles with 80% capacity retention, far surpassing NMCA (<320 cycles) and the reported NMA-based cathodes.